Tetrafluoroethylene (TFE) and a fluorovinyl ether (FVE) are copolymerized (to make the copolymer TFE/FVE) in aqueous medium according to the procedure described in U.S. Pat. No. 3,635,926. In this procedure, at the end of the reaction the polymerization vessel contains
1. A LIQUID PHASE COMPRISING WATER, THE COPOLYMER TFE/FVE dispersed in the water, and the usual polymerization additives such as surfactant, buffer, and initiator, and initiator decomposition products. Some FVE monomer, and fluorocarbon polymerization solvent (if such is employed) are present in this phase in emulsified form or adsorbed on the polymer if the polymerization vessel is under pressure,
2. A DENSER LIQUID PHASE COMPRISING UNREACTED FVE monomer and fluorocarbon polymerization solvent (if such is employed). Some TFE and chain transfer agent are present in this phase also,
3. A VAPOR PHASE COMPRISING MOSTLY UNREACTED TFE and some FVE, water vapor, gaseous chain transfer agent, and fluorocarbon polymerization solvent (if such is employed).
Several ways of recovering the copolymer and also recovering the TFE and FVE monomers have been tried or considered, but found impractical. These are:
A. WITHDRAWING THE WATER/COPOLYMER PHASE (1) UNDER AUTOGENOUS PRESSURE AND LEAVING PHASES (2) AND (3) IN THE VESSEL FOR THE NEXT POLYMERIZATION. This has two disadvantages; first, part of the expensive FVE is in phase (1) and remains unrecovered, and second, some polymer remains in the polymerization vessel, causing coagulum formation and resulting in oversize polymer particles in the next polymerization.
B. WITHDRAWING THE DENSER BOTTOM PHASE (2) UNDER AUTOGENOUS PRESSURE. This method has the disadvantage of leaving too much FVE in the other two phases. Also phase (2) contains some entrained copolymer, leaving the FVE contaminated with copolymer.
C. WITHDRAWING VAPOR PHASE (3), WHICH WILL DROP THE PRESSURE WITHIN THE VESSEL TO ABOUT THE VAPOR PRESSURE OF LIQUID PHASE (2). Liquid phase (2) then bubbles up through aqueous phase (1) until phase (2) is vaporized. The disadvantages of this procedure are several. First, the vapor phase cannot be separated merely by cooling because the water vapor in it will freeze and eventually ice-up the equipment. Also complete separation is difficult because of the likelihood of fogging, with the recoverable components left entrained in the vapor vent stream. In addition, the FVE, TFE and any solvent present cannot be recovered by adsorption on activated charcoal because it catalyzes the polymerization of TFE.
Thus, a practical way of recovering unreacted monomers from this copolymerization process is desirable.